<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box {
            height: 100px;
        }
        .a {
            margin-bottom: 30px;
            background-color: #007aff;
            position: absolute;
        }
        .b {
            margin-top: 20px;
            background-color: rebeccapurple;
            padding: 10px;
            border: 1px solid red;
        }
    </style>
</head>
<body>
<div>
    <div class="a box">
        <div>2</div>
    </div>
    <div class="b box">
        <div>3</div>
    </div>
</div>
<script>
    let f1 =  function(){
        var n=999;
        return function f2(){
            console.log(n++)
        }
    }

    let a = f1()

    f1 = null

    a()
    a()
    a()

    a = null


    console.log('ok')

    class A{
        aa = 1
        constructor () {
            console.log(this.aa)
        }
    }
    a = new A()
</script>
</body>
</html>
